1. Field of the Invention
The present invention relates to an air conditioner for a vehicle, and more particularly, to a method for controlling the operation of a compressor for preventing noise that occurs in case of the shortage of refrigerant flow caused by less discharge capacity of the compressor of an air conditioner for a vehicle.
2. Description of the Related Art
An air conditioner is installed to heat or cool an interior of a vehicle. In a cooling system of such an air conditioner, a swash plate type compressor is generally employed as a compressor for compressing a vapor refrigerant of low temperature and low pressure, which is introduced from an evaporator, into a high temperature and high pressure refrigerant and then transferring it to a condenser.
The swash plate type compressor is operated according to on/off of an air conditioner switch. If the compressor is operated, temperature of the evaporator is lowered, and if the compressor is stopped, the temperature of the evaporator is raised.
Meanwhile, swash plate type compressors are classified into a fixed capacity compressor and a variable capacity compressor. These compressors are operated by power transmitted from rotating force of a vehicle engine. Here, the fixed capacity compressor is provided with an electronic clutch to control the operation of the compressor.
However, in a case where the electronic clutch is provided, engine RPM may be varied when the compressor is operated or stopped, which may disturb stable running of the vehicle.
Thus, recently, a clutch is not provided, but the variable capacity compressor that is always operated while the engine is driven and capable of varying the refrigerant discharge capacity of by changing a slope of a swash plate of the compressor is used.
In such a variable capacity swash plate type compressor, a pressure control valve is generally used to control a slope of the swash plate to regulate the refrigerant discharge amount. In recent, a swash plate slope control valve (hereinafter, referred to as “ECV”), of which the operation is controlled in an electric manner, is used.
Thus, in a case where a variable capacity swash plate type compressor employing an ECV, the slope of the swash plate is changed by the duty of the ECV or an applied current value, and the refrigerant discharge amount of the compressor is determined depending on the slope of the swash.
As a result, it means that the duty of ECV or the applied current value is an important factor to determine the evaporator temperature (hereinafter, the case where the compressor operates means that the ECV duty is more than zero (0) and a refrigerant is discharged).
The aforementioned ECV duty is a percentage value exhibiting a time period, during which the ECV is on, per the entire time. Thus, in a case where the duty is high, the refrigerant discharge of the compressor increases, while in a case where the duty is low, the refrigerant discharge decreases.
FIG. 1 is a sectional view showing an inside configuration of a conventional variable capacity swash plate type compressor.
As shown in the figure, in a conventional variable capacity swash plate type compressor, a center bore 11 is formed through a center of a cylinder block 10, and a plurality of cylinder bores 13 are formed through the cylinder block 10 to radially surround the center bore 11. Also, a piston 15 is movably installed in each cylinder bore 13, thereby compressing a refrigerant in the cylinder bore 13.
Meanwhile, a front housing 20 is installed at one end of the cylinder block 10. The front housing 20 and the cylinder block 10 define a crank chamber 21 therein.
In addition, a rear housing 30 is installed at the other end of the cylinder block 10, i.e., at a side opposite to the front housing 20. A suction chamber 31 is formed in the rear housing to selectively communicate with the cylinder bore 13. At this time, the suction chamber 31 serves to transfer a refrigerant to be compressed into the cylinder bore 13.
Also, a discharge chamber 33 is formed in the rear housing 30. The discharge chamber 33 is formed in a region corresponding to a center of a side of the rear housing 30 that faces the cylinder block 10. The discharge chamber 33 gives a place where the refrigerant compressed in the cylinder bore 13 stays temporarily. A control valve 35 is provided at one side of the rear housing 30, wherein the control valve 35 controls an angle of a swash plate 48 which will be described later, by adjusting a degree of opening of a channel between the discharge chamber 33 and the crank chamber 21.
Meanwhile, a drive shaft 40 is rotatably installed through the center bore 11 of the cylinder block 10 and a shaft hole 23 of the front housing 20. The drive shaft 40 is rotated by driving force transferred from an engine. The drive shaft 40 is rotatably installed to the cylinder block 10 and the front housing 20 by a bearing 42.
Also, a rotor 44 is installed to the crank chamber 21 such that the drive shaft 40 passes through a center of the rotor and the rotor rotates together with the drive shaft 40. At this time, the rotor 44 is substantially disk-shaped and is fixed to the drive shaft 40. Also, a hinge arm 46 is formed to protrude on one side of the rotor 44.
A swash plate 48 is hinged to the rotor 44 and installed to the drive shaft 40 to rotate together with the drive shaft 40. The swash plate 48 is installed to the drive shaft 40 to have an angle changed according to discharge capacity of the compressor. In other words, the swash plate 40 is positioned between a state that it is perpendicular to a lengthwise direction of the drive shaft 40 and a state that it is inclined at a predetermined angle with respect to the drive shaft 40. The swash plate 48 has an edge connected to the pistons 15 through shoes 50. In other words, the edge of the swash plate 48 is connected to a connector 17 of the piston 15 through the shoe 50 such that the piston 15 is linearly reciprocated in the cylinder bore 13 by the rotation of the swash plate 48.
A connection arm 52 connected to the hinge arm 46 of the rotor 44 is formed to protrude on the swash plate 48. A hinge pin 54 is installed at a front end of the connection arm 52 in a direction perpendicular to the lengthwise direction of the connection arm 52, and the hinge pin 54 is movably hooked to a support 47 formed at a front end of the hinge arm 46 of the rotor 44.
A back spring 56 is installed to give elastic force between the rotor 44 and the swash plate 48. The back spring 56 is installed around an outer surface of the drive shaft 40 and gives elastic force in a direction in which a slope of the swash plate 48 decreases.
A swash plate stopper 58 is formed to protrude on one surface of the swash plate 48. The swash plate stopper 58 serves to regulate a degree of inclination of the swash plate 48 with respect to the drive shaft 40.
A shaft stopper 60 is provided at one end of the drive shaft 40. The shaft stopper 60 is installed around the outer surface of the drive shaft 40, and the shaft stopper 60 serves to regulate an installation location of the swash plate 48 when it erected in a direction perpendicular to the lengthwise direction of the drive shaft 40.
Meanwhile, Japanese Laid-open Patent Publication No. 2005-104305 discloses a technique of maximizing the discharge capacity of a compressor regardless of a target cooling temperature when a vehicle is decelerated such that deceleration energy may be maximally used as compressor driving energy when a vehicle is decelerated. However, in this technique, there is a problem in that the compressor discharge capacity is unnecessarily increased to the maximum to thereby hinder refrigerant from flowing smoothly.
In addition, when the refrigerant discharge amount of the compressor is small, the refrigerant may not circulate smoothly in the compressor if the above state is continued, which may cause noise.
Thus, the ECV duty is kept in a low state, so that noise is generated when flow rate of refrigerant of the compressor is small and the workability of the compressor is deteriorated, thereby causing a problem in use.